Second material with an emission shader making the scene darker
Clamping stops light from being brighter. So if you need a light with strength of 10000 and clamp it at 15, you lose most of its effect. Turn off clamping at first, set up lights for the scene and only then check the values in your render by right clicking and dragging on the render result(maybe render a small test area) to adjust your values for the clamping when fireflies become a problem. You should use higher values than the brightest fireflies in your render. The &quot;strange artifacts&quot; have replaced the &quot;strange noise&quot; in previous versions without denoising and simply means you do not have enough samples. Increase the amount of samples. You could also add bigger light sources to your scene to avoid noise/denoising artifacts. It might also make sense to have more max light bounces in an interior scene.